Hard weather conditions such as high wind speeds, have high impact on exposed wind turbines causing major loads on its components due to the excessive aero dynamical power of the wind acting on the wind turbine rotor.
Various methods of prior art have been used to cut-off the wind turbine from the grid e.g. at a predefined stop wind speed or to reduce the power and/or the rotational speed of the rotor proportional to an increase in wind speed above a predefined “roll off” wind speed.
EP 0847496 discloses a wind turbine control method implying that the power of the wind turbine as well as the rotor speed of a gear-less wind turbine is reduced continuously above and in dependence of a critical wind speed in order to avail the wind turbine to operate at an extended wind velocity range.
A problem related to this technique is that within the extended wind velocity range loads on wind turbine components such as the gear may be drastically increased. Furthermore for wind situations comprising high fluctuations in wind energy at the relevant high wind velocity may both appear very sudden and involve extreme sudden variations in the rotational speed of the wind turbine.
Fluctuations in wind energy may be less critical when applying the method in gear-less wind turbines while application in connection with a wind turbine including a gear is highly problematic as a continuous reduction of wind turbine rotor speed in relation to increasing wind velocity may require that the control is extremely fast as the possible fluctuations in energy increases critically while exceeding a certain point, e.g. 25 m/s.
It is an object of the present invention to provide an advantageous method of operating a wind turbine during high wind conditions without the above mentioned disadvantages.